Sampling process for combustion gases

ABSTRACT

A sampling process for combustion gases which includes the steps of introducing a continuous stream of ambient air into a conduit system, reducing the temperature of the ambient air to not more than about 40* F., subsequently heating the air to about 130* F., introducing exhaust gases into the system downstream from the heated air and mixing it with the heated air, passing the mixture of gases through a heat sink to obtain a uniform temperature, exhausting the gases from the heat sink at a constant volume, and drawing off a quantity of gas into a sample tube.

United States Patent [72] Inventor Allen Cleveland 5 3,304,783 2/1967 Quigley 73/4215 R Ann Arbor, Mich. 3,406,562 l/l968 Perna,.lr,et a1... 73/23 [21] Appl. No. 36,876 3,438,261 4/1969- Collins, Jr 73/4215 [22] Filed May 13, 1970 45 Patented Oct. 12, 1971 j l if f, 2? H [73] Assignee Olson Laboratories, Inc. Assistant 'r 2.?"

Dearbom Mich. ttorneyu en, ett e, Oman antor E E [54] SAMPLING PRO-C FOR COMBUSTION GAS 8 ABSTRACT: A sampling process for combustion gases which Claims, 1 Drawing Fig.

includes the steps of mtroducmg a continuous stream of am- [52] US. Cl 73/4215 R bi m i i t a ond it s st m educing the temperature of '3- Cl the ambient air to not more than about F., subsequently Fleld 0f Search 73/4215 R, h ti the i o ab ut F introducing exhaust gases into 23, the system downstream from the heated air and mixing it with the heated air, passing the mixture of gases through a heat sink [561 References cued to obtain a uniform temperature, exhausting the gases from UNITED STATES PATENTS the heat sink at a constant volume, and drawing off a quantity 2,955,457 10/1960 Peters et al. 73/4215 X of gas into a sample tube.

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III:

SAMPLING PROCESS FOR COMBUSTION GASES BACKGROUND OF THE INVENTION This invention relates to a process of sampling exhaust gases to determine the constituents therein including nitrogen oxide. It is well known that exhaust gases, particularly exhaust gases from internal combustion engines, are a major source of atmospheric pollution in the United States. Efforts are currently being made and will be made in thefuture to reduce the pollution to the atmosphere caused by exhaust gases.

ln general, combustion engine exhaust gases contain hydrocarbons, carbon monoxide and nitrogen oxide compounds. Some suggested solutions for the pollution problem include recycling of the exhaust gases back through the carburetor in order to obtain more complete burning of the gases, and also attaching refractory mufflers or other devices to the exhaust system to cause more complete combustion of the exhaust gases. In order to measure the effectiveness of these devices, it is necessary to be able to determine accurately the quantities of the various components of the exhaust gases. Heretofore, it has been possible to measure the amount of carbon monoxide and hydrocarbons being emitted in the exhaust gases but it has not been possible to accurately measure the amount of nitrogen oxides present.

it is an object of this invention to provide a process of sampling which enables the nitrogen oxides content of exhaust gases to be accurately measured.

lt is another object of this invention to provide a simple and economic method of sampling exhaust gases which enables the nitrogen oxides content to be accurately determined.

These and other objects of the invention will be understood by reference to the following specification and drawing, in which:

P16. 1 is a somewhat schematic flow chart of the method of the invention.

SUMMARY OF THE INVENTION The method of the invention comprises introducing a continuous stream of ambient air into a conduit system, reducing the temperature of the ambient air to not more than about 40 F., subsequently heating the air to about 130 F., introducing exhaust gases into the system and mixing it with the heated air, passing the mixture of gases through a heat sink to even out temperature fluctuations, exhausting the gases from the heat sink at a constant volume, and drawing off a quantity of gas into a sample tube.

The method of this invention provides a sample of constant mass in terms of temperature, volume, and moisture content which can then be inserted into a measuring instrument reading in percentage part per million or similar proportional measurement to determine the mass per unit of time of nitrogen oxides present in the sample.

DESCRIPTION OF THE PREFERRED EMBODIMENT The method of the invention is illustrated somewhat schematically in FIG. I. In the first step of the method of the invention, ambient air, normally about 70 F., is drawn through an air filter l and into a conduit 12, attached to the bottom of the air filter 10. The air is then passed from the conduit 12 to an air cooler 14 where the temperature of the air is reduced, moisture which may be present, is condensed and drains out the bottom of the air cooler 14. The cooled air is then passed into a conduit 16 and through an electric heater 18 which is used to heat the air back up to a temperature of about 130 F. The heated air is then passed into a conduit 20 which is intersected by another conduit 22 through which exhaust gases are being passed.

The exhaust gases and the heated air are mixed in the conduit 22 and conduit 20. The exhaust gas-heated air mixture averages about 130 F. from a low of about 90 F. to a high of 250 F. at this point. The exhaust gas to heated air ratio in the system downstream from the intersection of the conduit 22 carrying the exhaust gas with conduit 20 ranges from l to 1-20 parts by volume and averages 1-10 parts. The exhaust gas-heated air mixture is then fed into a heat sink 24 which serves to average out the temperature of the mixture from the high and low peaks, The temperature of the exhaust gasheated air mixture after it passes through the heat sink varies about its average by no more than 150 F.

From the heat sink, the air-exhaust gas mixture is passed into a conduit 26 and is drawn out by a pump 28 through a stack 30 at a constant volume rate of about 300 cubic feet per minute.

A smaller sampling tube conduit 32 connects with the conduit 26, in such a manner that it samples the homogenous filtered air-exhaust gas mix. The sample drawn off through the sample tube 32 is then analyzed for nitrogen oxides, carbon monoxide and hydrocarbons.

The sample being drawn off through the sample tube is of constant mass in terms of uniform temperature, constant volume and has a moisture content below the dewpoint.

A thermal switch 34 is situated in the conduit 26 downstream from the heat sink 24. The thermal switch 34 is connected by conduit 36 to the electric heater 18 so that when the temperature of the exhaust gas-air mixture in the conduit 26 rises above the desired level through addition of exhaust heat, the electric heater is deenergized for the length of time required to maintain a constant level of temperatures throughout the test.

In order to obtain an accurate reading of the quantity of nitrogen oxides present in the exhaust gas, it is necessary to reduce the temperature of the ambient air in the air cooler to about 40 F. in order to remove a significant quantity of moisture therefrom. This is because nitrogen oxides are water soluble and if the ambient air was introduced into the presence of the exhaust gases without first being demoistured, condensation would occur at the junction of conduit 22 with conduit 20, the nitrogen oxides would be dissolved in the condensation, and an inaccurate reading would result when the sample was removed through the sample tube. By reducing the temperature of the ambient air to less than about 40 F., however, and condensing the moisture present therein in the air cooler, the subsequently heated air coming into contact with the exhaust gas will not cause the moisture in the exhaust gas to condense because the dewpoint of the mixture of the heated air and exhaust gases will be too low for condensation to occur.

Thus, the crux of the method if the invention is to remove sufficient moisture from the ambient air before it is admixed with the exhaust gases to preclude moisture condensation from occurring as a result of the air being admixed with the exhaust gases. In general, when automobile exhaust gases are being sampled, it has been found necessary to cool the ambient air to at least 40 F. in order that no subsequent moisture condensation will occur when the subsequently heated air and the exhaust gases are admixed.

What is claimed is:

l. A sampling process for combustion gases which comprises:

a. introducing a continuous stream of ambient air into a conduit system, reducing the temperature of the ambient air in the system to not more than about 40 F., thereby causing moisture in the air to condense out,

. heating the air to about F.,

. introducing exhaust gases into the system and mixing it with the heated air,

. passing the mixture of gases through a heat sink to obtain a uniform temperature,

f. exhausting the gases from the heat sink at a constant volume,

. drawing off a quantity of gas into a sample tube, whereby a sample of constant mass in terms of temperature, and volume, and at a water content below the dewpoint is provided.

2. The method of claim 1 wherein the ratio of exhaust gases to air introduced into the system ranges from 1-5 to l20.

3,61 1,812 3 4 3. The method of claim 1 wherein the temperature of the from the heat sink at the rate of about 300 feet per minute.

gases in the heat sink varies not more than 50 F. from 5. The method of claim I wherein the exhaust gases are inaveragetroduced into the system at an average of 130 F.

4. The method of claim 1 wherein the gases are exhausted 

2. The method of claim 1 wherein the ratio of exhaust gases to air introduced into the system ranges from 1-5 to 1-20.
 3. The method of claim 1 wherein the temperature of the gases in the heat sink varies not more than 50* F. from average.
 4. The method of claim 1 wherein the gases are exhausted from the heat sink at the rate of about 300 feet per minute.
 5. The method of claim 1 wherein the exhaust gases are introduced into the system at an average of 130* F. 